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Hemingway HW, Richey RE, Moore AM, Saul BM, Shokraeifard AM, Cope HL, Olivencia-Yurvati AH, Cunningham RL, Smith ML, Romero SA. Effect of acute heat exposure on the pressor response to a voluntary hypoxic apnea. J Appl Physiol (1985) 2023; 135:542-548. [PMID: 37439242 PMCID: PMC10538993 DOI: 10.1152/japplphysiol.00245.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 07/10/2023] [Accepted: 07/11/2023] [Indexed: 07/14/2023] Open
Abstract
The pressor response induced by a voluntary hypoxic apnea is mediated largely by increased sympathetic outflow. The neural control of blood pressure is altered in recovery from acute heat exposure, but its effect on the pressor response to a voluntary hypoxic apnea has never been explored. Therefore, we tested the hypothesis that prior heat exposure would attenuate the pressor response induced by a voluntary hypoxic apnea. Eleven healthy adults (five women) were exposed to whole body passive heating (water-perfused suit) sufficient to increase body core temperature by 1.2°C. Voluntary hypoxic apneas were performed at baseline and in recovery when body core temperature returned to ≤ 0.3°C of baseline. Participants breathed gas mixtures of varying [Formula: see text] (21%, 16%, and 12%; randomized) for 1 min followed by a 15-s end-expiratory apnea. The change in arterial oxygen saturation during each apnea did not differ from baseline to recovery (P = 0.6 for interaction), whereas the pressor response induced by a voluntary hypoxia apnea was reduced ([Formula: see text] 21%, baseline 17 ± 7 mmHg vs. recovery 14 ± 7 mmHg; [Formula: see text] 16%, baseline 24 ± 8 mmHg vs. recovery 18 ± 7 mmHg; [Formula: see text] 12%, baseline 28 ± 11 mmHg vs. recovery 24 ± 11 mmHg; P = 0.01 for main effect of time). These data suggest that prior heat exposure induces a cross-stressor effect such that the pressor response to a voluntary hypoxic apnea is attenuated.NEW & NOTEWORTHY The pressor response induced by a voluntary hypoxic apnea is mediated by increased sympathetic outflow. The neural control of blood pressure is altered in recovery from acute heat exposure, but its effect on the pressor response to a voluntary hypoxic apnea has never been explored. Our data suggest that prior heat exposure induces a cross-stressor effect such that the pressor response to a voluntary hypoxic apnea is attenuated.
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Affiliation(s)
- Holden W Hemingway
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Rauchelle E Richey
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Amy M Moore
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Benjamin M Saul
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Austin M Shokraeifard
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Heidi L Cope
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Albert H Olivencia-Yurvati
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
- Department of Surgery, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Rebecca L Cunningham
- Department of Pharmaceutical Sciences, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Michael L Smith
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Steven A Romero
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
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A Methodological Perspective on the Function and Assessment of Peripheral Chemoreceptors in Heart Failure: A Review of Data from Clinical Trials. Biomolecules 2022; 12:biom12121758. [PMID: 36551186 PMCID: PMC9775522 DOI: 10.3390/biom12121758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 11/22/2022] [Accepted: 11/24/2022] [Indexed: 11/29/2022] Open
Abstract
Augmented peripheral chemoreceptor sensitivity (PChS) is a common feature of many sympathetically mediated diseases, among others, and it is an important mechanism of the pathophysiology of heart failure (HF). It is related not only to the greater severity of symptoms, especially to dyspnea and lower exercise tolerance but also to a greater prevalence of complications and poor prognosis. The causes, mechanisms, and impact of the enhanced activity of peripheral chemoreceptors (PChR) in the HF population are subject to intense research. Several methodologies have been established and utilized to assess the PChR function. Each of them presents certain advantages and limitations. Furthermore, numerous factors could influence and modulate the response from PChR in studied subjects. Nevertheless, even with the impressive number of studies conducted in this field, there are still some gaps in knowledge that require further research. We performed a review of all clinical trials in HF human patients, in which the function of PChR was evaluated. This review provides an extensive synthesis of studies evaluating PChR function in the HF human population, including methods used, factors potentially influencing the results, and predictors of increased PChS.
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3
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Limberg JK, Baker SE, Ott EP, Jacob DW, Scruggs ZM, Harper JL, Manrique-Acevedo CM. Endothelin-1 receptor blockade does not alter the sympathetic and hemodynamic response to acute intermittent hypoxia in men. J Appl Physiol (1985) 2022; 133:867-875. [PMID: 35952348 PMCID: PMC9560055 DOI: 10.1152/japplphysiol.00837.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 07/18/2022] [Accepted: 08/08/2022] [Indexed: 11/22/2022] Open
Abstract
Repeat exposures to low oxygen (intermittent hypoxia, IH), like that observed in sleep apnea, elicit increases in muscle sympathetic nerve activity (MSNA) and blood pressure (BP) in men. Endothelin (ET) receptor antagonists can attenuate the sympathetic and BP response to IH in rodents; whether these data translate to humans are unclear. We hypothesized that ET-receptor antagonism would ameliorate any rise in MSNA and BP following acute IH in humans. Twelve healthy men (31 ± 1 yr) completed two visits (control, bosentan) separated by at least 1 wk. MSNA, BP, and baroreflex sensitivity (modified Oxford) were assessed during normoxic rest before and following 30 min of IH. The midpoint (T50) for each individual's baroreflex curve was calculated. Acute IH increased plasma ET-1 (P < 0.01), MSNA burst frequency (P = 0.03), and mean BP (P < 0.01). There was no effect of IH on baroreflex sensitivity (P = 0.46), although an increase in T50 was observed (P < 0.01). MSNA burst frequency was higher (P = 0.04) and mean BP (P < 0.01) was lower following bosentan treatment compared with control. There was no effect of bosentan on baroreflex sensitivity (P = 0.53), although a lower T50 was observed on the bosentan visit (P < 0.01). There was no effect of bosentan on increases in MSNA (P = 0.81) or mean BP (P = 0.12) following acute IH. Acute IH results in an increase in ET-1, MSNA, and BP in healthy young men. The effect of IH on MSNA and BP is not attenuated following ET-receptor inhibition. Present data suggest that acute IH does not increase MSNA or BP through activation of ET-receptors in healthy young men.NEW & NOTEWORTHY Repeat exposures to low oxygen (intermittent hypoxia, IH) elicit increases in muscle sympathetic nerve activity (MSNA) and blood pressure (BP) in men. Endothelin (ET) receptor antagonists can attenuate the sympathetic and BP response to IH in rodents; whether these data translate to humans were unclear. We show acute IH results in an increase in ET-1, MSNA, and BP in healthy young men; however, the effect of IH on MSNA and BP does not occur through activation of ET-receptors in healthy young men.
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Affiliation(s)
- Jacqueline K Limberg
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | - Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | | | - Jennifer L Harper
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Camila M Manrique-Acevedo
- Department of Medicine, University of Missouri, Columbia, Missouri
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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4
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Panza GS, Puri S, Lin HS, Mateika JH. Divergent Ventilatory and Blood Pressure Responses are Evident Following Repeated Daily Exposure to Mild Intermittent Hypoxia in Males with OSA and Hypertension. Front Physiol 2022; 13:897978. [PMID: 35721527 PMCID: PMC9204590 DOI: 10.3389/fphys.2022.897978] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 05/03/2022] [Indexed: 11/17/2022] Open
Abstract
Introduction: Resting minute ventilation and ventilation during and following hypoxia may be enhanced following daily exposure to mild intermittent hypoxia (MIH). In contrast, resting systolic blood pressure (SBP) is reduced following daily exposure to MIH. However, it is presently unknown if the reduction in resting SBP following daily exposure, is coupled with reduced SBP responses during and after acute exposure to MIH. Methods: Participants with obstructive sleep apnea (OSA) and hypertension (n = 10) were exposed to twelve 2-min bouts of MIH (oxygen saturation—87%)/day for 15 days. A control group (n = 6) was exposed to a sham protocol during which compressed air (i.e., FIO2 = 0.21) was inspired in place of MIH. Results: The hypoxic ventilatory response (HVR) and hypoxic systolic blood pressure response (HSBP) increased from the first to the last hypoxic episode on the initial (HVR: 0.08 ± 0.02 vs. 0.13 ± 0.02 L/min/mmHg, p = 0.03; HSBP: 0.13 ± 0.04 vs. 0.37 ± 0.06 mmHg/mmHg, p < 0.001) and final (HVR: 0.10 ± 0.01 vs. 0.15 ± 0.03 L/min/mmHg, p = 0.03; HSBP: 0.16 ± 0.03 vs. 0.41 ± 0.34 mmHg/mmHg, p < 0.001) day. The magnitude of the increase was not different between days (p ≥ 0.83). Following exposure to MIH, minute ventilation and SBP was elevated compared to baseline on the initial (MV: 16.70 ± 1.10 vs. 14.20 ± 0.28 L/min, p = 0.01; SBP: 167.26 ± 4.43 vs. 151.13 ± 4.56 mmHg, p < 0.001) and final (MV: 17.90 ± 1.25 vs. 15.40 ± 0.77 L/min, p = 0.01; SBP: 156.24 ± 3.42 vs. 137.18 ± 4.17 mmHg, p < 0.001) day. The magnitude of the increases was similar on both days (MV: 3.68 ± 1.69 vs. 3.22 ± 1.27 L/min, SBP: 14.83 ± 2.64 vs. 14.28 ± 1.66 mmHg, p ≥ 0.414). Despite these similarities, blood pressure at baseline and at other time points during the MIH protocol was reduced on the final compared to the initial day (p ≤ 0.005). Conclusion: The ventilatory and blood pressure responses during and following acute MIH were similar on the initial and final day of exposure. Alternatively, blood pressure was down regulated, while ventilation was similar at all time points (i.e., baseline, during and following MIH) after daily exposure to MIH.
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Affiliation(s)
- Gino S Panza
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, United States.,Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Shipra Puri
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, United States.,Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Ho-Sheng Lin
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, United States.,Department of Otolaryngology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Jason H Mateika
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, United States.,Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States.,Department of Internal Medicine, Wayne State University School of Medicine, Detroit, MI, United States
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Keough JRG, Tymko MM, Boulet LM, Jamieson AN, Day TA, Foster GE. Cardiorespiratory plasticity in humans following two patterns of acute intermittent hypoxia. Exp Physiol 2021; 106:1524-1534. [PMID: 34047414 DOI: 10.1113/ep089443] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 05/25/2021] [Indexed: 01/02/2023]
Abstract
NEW FINDINGS What is the central question of this study? Do cardiorespiratory experience-dependent effects (EDEs) differ between two different stimulus durations of acute isocapnic intermittent hypoxia (IHx; 5-min vs. 90-s cycles between hypoxia and normoxia)? What is the main finding and its importance? There was long-term facilitation in ventilation and blood pressure in both IHx protocols, but there was no evidence of progressive augmentation or post-hypoxia frequency decline. Not all EDEs described in animal models translate to acute isocapnic IHx responses in humans, and cardiorespiratory responses to 5-min versus 90-s on/off IHx protocols are largely similar. ABSTRACT Peripheral respiratory chemoreceptors monitor breath-by-breath changes in arterial CO2 and O2 , and mediate ventilatory changes to maintain homeostasis. Intermittent hypoxia (IHx) elicits hypoxic ventilatory responses, with well-described experience-dependent effects (EDEs), derived mostly from animal work involving intermittent 5-min cycles of hypoxia and normoxia. These EDEs include post-hypoxia frequency decline (PHxFD), progressive augmentation (PA) and long-term facilitation (LTF). Comparisons of these EDEs between animal models and humans using similar IHx protocols are lacking. In addition, it is unknown whether shorter bouts of hypoxia, which may be more relevant to clinical conditions, elicit EDEs of similar magnitudes in humans. Respiratory (frequency, tidal volume and minute ventilation ( V ̇ I ) and cardiovascular (heart rate and mean arterial pressure (MAP)) variables were measured during and following two patterns of acute isocapnic IHx in 14 healthy human participants (four female): (1) 5 × 5 min and (2) 5 × 90 s on/off hypoxia. Participants' end-tidal P O 2 was clamped at 45 Torr during hypoxia and 100 Torr during normoxia. We found that (1) PHxFD and PA were not present in either IHx pattern (P > 0.14), (2) LTF was present in V ̇ I following both 5-min (P < 0.001) and 90-s isocapnic IHx trials (P < 0.001), and (3) LTF was present in MAP following 5-min isocapnic IHx (P < 0.001), and trended towards significance following 90-s IHx (P = 0.058). We demonstrate that acute isocapnic IHx alone may not elicit all of the EDEs that have been described in animal models. Additionally, ventilatory LTF occurred regardless of the length of hypoxia-normoxia cycles.
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Affiliation(s)
- Joanna R G Keough
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada.,Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Lindsey M Boulet
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.,Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Alenna N Jamieson
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Glen E Foster
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
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6
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Wong B, Tong JY, Schulz AM, Graham SL, Farah CS, Fraser CL. The impact of continuous positive airway pressure treatment on retinal vascular changes in obstructive sleep apnea. J Clin Sleep Med 2021; 17:983-991. [PMID: 33533333 DOI: 10.5664/jcsm.9118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
STUDY OBJECTIVES Obstructive sleep apnea (OSA) was recently shown to be associated with quantifiable retinal vascular changes, which correlate with disease severity. This follow-up study examines the response of retinal vascular changes in patients with OSA receiving continuous positive airway pressure (CPAP) treatment. METHODS This prospective cohort study recruited adult patients undergoing diagnostic polysomnography at a tertiary sleep clinic in Sydney, Australia, stratified into 4 groups by the apnea-hypopnea index; control patients and patients with mild, moderate, and severe OSA. At baseline and follow-up approximately 24 months later, static retinal vascular calibers were derived from fundus photographs, and dynamic vascular pulsation amplitudes were measured on video fundoscopy. A proportion of patients started CPAP therapy after baseline assessment. RESULTS Seventy-nine patients participated in this follow-up study: 9 control patients and 18 patients with mild OSA, 21 patients with moderate OSA, and 31 patients with severe OSA. Twenty-five patients started CPAP after baseline. In the severe group, patients not on treatment showed progressive narrowing of retinal arteries from baseline, whereas those on CPAP showed a slight improvement (mean, 171.3-165.1 and 171.2-174.0 μm, respectively; P = .012). Arterio-venous ratio was also significantly reduced in the nontreatment group compared to the treatment group in those with severe OSA (0.836-0.821 and 0.837-0.855, respectively; P = .031). CPAP did not seem to have a significant impact on venous caliber or vascular pulsatility. CONCLUSIONS This study shows that patients with severe untreated OSA demonstrate progressive retinal arterial narrowing, whereas CPAP treatment may be protective.
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Affiliation(s)
- Brendon Wong
- Department of Ophthalmology and Vision Science, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia.,Save Sight Institute, University of Sydney, Sydney, New South Wales, Australia
| | - Jessica Y Tong
- Department of Ophthalmology and Vision Science, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Angela M Schulz
- Department of Ophthalmology and Vision Science, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Stuart L Graham
- Department of Ophthalmology and Vision Science, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Claude S Farah
- Macquarie University Respiratory and Sleep, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia.,Concord Clinical School, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia
| | - Clare L Fraser
- Department of Ophthalmology and Vision Science, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales, Australia.,Save Sight Institute, University of Sydney, Sydney, New South Wales, Australia
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7
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Puri S, Panza G, Mateika JH. A comprehensive review of respiratory, autonomic and cardiovascular responses to intermittent hypoxia in humans. Exp Neurol 2021; 341:113709. [PMID: 33781731 PMCID: PMC8527806 DOI: 10.1016/j.expneurol.2021.113709] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/17/2021] [Accepted: 03/24/2021] [Indexed: 01/08/2023]
Abstract
This review explores forms of respiratory and autonomic plasticity, and associated outcome measures, that are initiated by exposure to intermittent hypoxia. The review focuses primarily on studies that have been completed in humans and primarily explores the impact of mild intermittent hypoxia on outcome measures. Studies that have explored two forms of respiratory plasticity, progressive augmentation of the hypoxic ventilatory response and long-term facilitation of ventilation and upper airway muscle activity, are initially reviewed. The role these forms of plasticity might have in sleep disordered breathing are also explored. Thereafter, the role of intermittent hypoxia in the initiation of autonomic plasticity is reviewed and the role this form of plasticity has in cardiovascular and hemodynamic responses during and following intermittent hypoxia is addressed. The role of these responses in individuals with sleep disordered breathing and spinal cord injury are subsequently addressed. Ultimately an integrated picture of the respiratory, autonomic and cardiovascular responses to intermittent hypoxia is presented. The goal of the integrated picture is to address the types of responses that one might expect in humans exposed to one-time and repeated daily exposure to mild intermittent hypoxia. This form of intermittent hypoxia is highlighted because of its potential therapeutic impact in promoting functional improvement and recovery in several physiological systems.
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Affiliation(s)
- Shipra Puri
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America
| | - Gino Panza
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America
| | - Jason H Mateika
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI 48201, United States of America; Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, United States of America; Department of Internal Medicine, Wayne State University School of Medicine, Detroit, MI 48201, United States of America.
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8
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Jacob DW, Ott EP, Baker SE, Scruggs ZM, Ivie CL, Harper JL, Manrique-Acevedo CM, Limberg JK. Sex differences in integrated neurocardiovascular control of blood pressure following acute intermittent hypercapnic hypoxia. Am J Physiol Regul Integr Comp Physiol 2020; 319:R626-R636. [PMID: 32966122 DOI: 10.1152/ajpregu.00191.2020] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Repetitive hypoxic apneas, similar to those observed in sleep apnea, result in resetting of the sympathetic baroreflex to higher blood pressures (BP). This baroreflex resetting is associated with hypertension in preclinical models of sleep apnea (intermittent hypoxia, IH); however, the majority of understanding comes from males. There are data to suggest that female rats exposed to IH do not develop high BP. Clinical data further support sex differences in the development of hypertension in sleep apnea, but mechanistic data are lacking. Here we examined sex-related differences in the effect of IH on sympathetic control of BP in humans. We hypothesized that after acute IH we would observe a rise in muscle sympathetic nerve activity (MSNA) and arterial BP in young men (n = 30) that would be absent in young women (n = 19). BP and MSNA were measured during normoxic rest before and after 30 min of IH. Baroreflex sensitivity (modified Oxford) was evaluated before and after IH. A rise in mean BP following IH was observed in men (+2.0 ± 0.7 mmHg, P = 0.03), whereas no change was observed in women (-2.7 ± 1.2 mmHg, P = 0.11). The elevation in MSNA following IH was not different between groups (4.7 ± 1.1 vs. 3.8 ± 1.2 bursts/min, P = 0.65). Sympathetic baroreflex sensitivity did not change after IH in either group (P > 0.05). Our results support sex-related differences in the effect of IH on neurovascular control of BP and show that any BP-raising effects of IH are absent in young women. These data enhance our understanding of sex-specific mechanisms that may contribute to BP changes in sleep apnea.
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Affiliation(s)
- Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | - Clayton L Ivie
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Jennifer L Harper
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Camila M Manrique-Acevedo
- Department of Medicine, University of Missouri, Columbia, Missouri.,Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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9
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Ott EP, Jacob DW, Baker SE, Holbein WW, Scruggs ZM, Shoemaker JK, Limberg JK. Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans. Am J Physiol Regul Integr Comp Physiol 2020; 318:R961-R971. [PMID: 32267729 DOI: 10.1152/ajpregu.00004.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence (P < 0.01), AP incidence (P = 0.01), and AP content per burst (P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once (P < 0.01) and more than once (P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH (P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst (P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.
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Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | | | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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10
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Roy A, Farnham MMJ, Derakhshan F, Pilowsky PM, Wilson RJA. Acute intermittent hypoxia with concurrent hypercapnia evokes P2X and TRPV1 receptor-dependent sensory long-term facilitation in naïve carotid bodies. J Physiol 2018; 596:3149-3169. [PMID: 29159869 PMCID: PMC6068228 DOI: 10.1113/jp275001] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Accepted: 11/16/2017] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Activity-dependent plasticity can be induced in carotid body (CB) chemosensory afferents without chronic intermittent hypoxia (CIH) preconditioning by acute intermittent hypoxia coincident with bouts of hypercapnia (AIH-Hc). Several properties of this acute plasticity are shared with CIH-dependent sensory long-term facilitation (LTF) in that induction is dependent on 5-HT, angiotensin II, protein kinase C and reactive oxygen species. Several properties differ from CIH-dependent sensory LTF; H2 O2 appears to play no part in induction, whereas maintenance requires purinergic P2X2/3 receptor activation and is dependent on transient receptor potential vanilloid type 1 (TRPV1) receptor sensitization. Because P2X2/3 and TRPV1 receptors are located in carotid sinus nerve (CSN) terminals but not presynaptic glomus cells, a primary site of the acute AIH-Hc induced sensory LTF appears to be postsynaptic. Our results obtained in vivo suggest a role for TRPV1-dependent CB activity in acute sympathetic LTF. We propose that P2X-TRPV1-receptor-dependent sensory LTF may constitute an important early mechanism linking sleep apnoea with hypertension and/or cardiovascular disease. ABSTRACT Apnoeas constitute an acute existential threat to neonates and adults. In large part, this threat is detected by the carotid bodies, which are the primary peripheral chemoreceptors, and is combatted by arousal and acute cardiorespiratory responses, including increased sympathetic output. Similar responses occur with repeated apnoeas but they continue beyond the last apnoea and can persist for hours [i.e. ventilatory and sympathetic long-term facilitation (LTF)]. These long-term effects may be adaptive during acute episodic apnoea, although they may prolong hypertension causing chronic cardiovascular impairment. We report a novel mechanism of acute carotid body (CB) plasticity (sensory LTF) induced by repeated apnoea-like stimuli [i.e. acute intermittent hypoxia coincident with bouts of hypercapnia (AIH-Hc)]. This plasticity did not require chronic intermittent hypoxia preconditioning, was dependent on P2X receptors and protein kinase C, and involved heat-sensitive transient receptor potential vanilloid type 1 (TRPV1) receptors. Reactive oxygen species (O2 ·¯) were involved in initiating plasticity only; no evidence was found for H2 O2 involvement. Angiotensin II and 5-HT receptor antagonists, losartan and ketanserin, severely reduced CB responses to individual hypoxic-hypercapnic challenges and prevented the induction of sensory LTF but, if applied after AIH-Hc, failed to reduce plasticity-associated activity. Conversely, TRPV1 receptor antagonism had no effect on responses to individual hypoxic-hypercapnic challenges but reduced plasticity-associated activity by ∼50%. Further, TRPV1 receptor antagonism in vivo reduced sympathetic LTF caused by AIH-Hc, although only if the CBs were functional. These data demonstrate a new mechanism of CB plasticity and suggest P2X-TRPV1-dependent sensory LTF as a novel target for pharmacological intervention in some forms of neurogenic hypertension associated with recurrent apnoeas.
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Affiliation(s)
- Arijit Roy
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
| | | | - Fatemeh Derakhshan
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
| | | | - Richard J. A. Wilson
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
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11
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Mallet RT, Manukhina EB, Ruelas SS, Caffrey JL, Downey HF. Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential. Am J Physiol Heart Circ Physiol 2018; 315:H216-H232. [PMID: 29652543 DOI: 10.1152/ajpheart.00060.2018] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.
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Affiliation(s)
- Robert T Mallet
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - Eugenia B Manukhina
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas.,Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences , Moscow , Russian Federation.,School of Medical Biology South Ural State University , Chelyabinsk , Russian Federation
| | - Steven Shea Ruelas
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - James L Caffrey
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - H Fred Downey
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas.,School of Medical Biology South Ural State University , Chelyabinsk , Russian Federation
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12
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Affiliation(s)
- Marat Fudim
- Division of Cardiology, Department of Internal Medicine, Duke University Hospital, Durham, NC
| | - Adrian F Hernandez
- Division of Cardiology, Department of Internal Medicine, Duke University Hospital, Durham, NC
- Duke Cardiovascular Research Institute, Durham, NC
| | - G Michael Felker
- Division of Cardiology, Department of Internal Medicine, Duke University Hospital, Durham, NC
- Duke Cardiovascular Research Institute, Durham, NC
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13
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Jouett NP, Moralez G, Raven PB, Smith ML. Losartan reduces the immediate and sustained increases in muscle sympathetic nerve activity after hyperacute intermittent hypoxia. J Appl Physiol (1985) 2017; 122:884-892. [DOI: 10.1152/japplphysiol.00683.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 12/21/2016] [Accepted: 01/08/2017] [Indexed: 11/22/2022] Open
Abstract
Obstructive sleep apnea (OSA) is characterized by intermittent hypoxemia, which produces elevations in sympathetic nerve activity (SNA) and associated hypertension in experimental models that persist beyond the initial exposure. We tested the hypotheses that angiotensin receptor blockade in humans using losartan attenuates the immediate and immediately persistent increases in 1) SNA discharge and 2) mean arterial pressure (MAP) after hyperacute intermittent hypoxia training (IHT) using a randomized, placebo-controlled, repeated-measures experimental design. We measured ECG and photoplethysmographic arterial pressure in nine healthy human subjects, while muscle SNA (MSNA) was recorded in seven subjects using microneurography. Subjects were exposed to a series of hypoxic apneas in which they inhaled two to three breaths of nitrogen, followed by a 20-s apnea and 40 s of room air breathing every minute for 20 min. Hyperacute IHT produced substantial and persistent elevations in MSNA burst frequency (baseline: 15.3 ± 1.8, IHT: 24 ± 1.5, post-IHT 20.0 ± 1.3 bursts/min, all P < 0.01) and MAP (baseline: 89.2 ± 3.3, IHT: 92.62 ± 3.1, post-IHT: 93.83 ± 3.1 mmHg, all P < 0.02). Losartan attenuated the immediate and sustained increases in MSNA (baseline: 17.3 ± 2.5, IHT: 18.6 ± 2.2, post-IHT 20.0 ± 1.3 bursts/min, all P < 0.001) and MAP (baseline: 81.9 ± 2.6, IHT: 81.1 ± 2.8, post-IHT: 81.3 ± 3.0 mmHg, all P > 0.70). This investigation confirms the role of angiotensin II type 1a receptors in the immediate and persistent sympathoexcitatory and pressor responses to IHT. NEW & NOTEWORTHY This study demonstrates for the first time in humans that losartan, an angiotensin receptor blocker (ARB), abrogates the acute and immediately persistent increases in muscle sympathetic nerve activity and arterial pressure in response to acute intermittent hypoxia. This investigation, along with others, provides important beginning translational evidence for using ARBs in treatment of the intermittent hypoxia observed in obstructive sleep apnea patients.
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Affiliation(s)
- Noah P. Jouett
- Institute for Cardiovascular and Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas; and
| | - Gilbert Moralez
- Institute for Environmental and Exercise Medicine, Texas Health Presbyterian Hospital, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Peter B. Raven
- Institute for Cardiovascular and Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas; and
| | - Michael L. Smith
- Institute for Cardiovascular and Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas; and
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14
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Kahwash R, Khayat RN. A Practical Approach to the Identification and Management of Sleep-Disordered Breathing in Heart Failure Patients. Sleep Med Clin 2017; 12:205-219. [PMID: 28477775 DOI: 10.1016/j.jsmc.2017.01.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Sleep-disordered breathing (SDB) is a major health problem affecting much of the general population. Although SDB is responsible for rapid progression of heart failure (HF) and the worsening morbidity and mortality, advanced HF state is associated with accelerated development of SDB. In the face of recent developments in SDB treatment and availability of effective therapeutic options known to improve quality of life, exercise tolerance, and heart function, most HF patients with SDB are left unrecognized and untreated. This article provides an overview of SDB in HF with focus on practical approaches intended to facilitate screening and treatment.
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Affiliation(s)
- Rami Kahwash
- Section of Heart Failure and Transplant, Division of Cardiovascular Medicine, Davis Heart & Lung Research Institute, The Ohio State University, 473 West 12th Avenue, Columbus, OH 43210, USA.
| | - Rami N Khayat
- Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, Davis Heart & Lung Research Institute, The Ohio State University, 473 West 12th Avenue, Columbus, OH 43210, USA
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15
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Khayat R, Pleister A. Consequences of Obstructive Sleep Apnea: Cardiovascular Risk of Obstructive Sleep Apnea and Whether Continuous Positive Airway Pressure Reduces that Risk. Sleep Med Clin 2017; 11:273-86. [PMID: 27542874 DOI: 10.1016/j.jsmc.2016.05.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Obstructive sleep apnea (OSA) is present in up to 25% of otherwise healthy individuals. OSA is associated with intermittent hypoxia, oxidative stress, sympathetic activation, and an inflammatory response. These perturbations mediate the role of OSA as an independent and modifiable risk factor for cardiovascular disease (CVD). OSA can induce CVD or accelerate the progression of CVD into an end-stage disorder, including heart failure and stroke. Current clinical recommendations are based on existing clinical trial data and the clinical experience of our program; current and future clinical trials will help to optimize management of OSA in the setting of CVD.
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Affiliation(s)
- Rami Khayat
- Internal Medicine-Pulmonary, Allergy, Critical Care, and Sleep Medicine, Wexner Medical Center, The Ohio State University, Suite 200, 473 West 12th Avenue, Columbus, OH 43210-1267, USA
| | - Adam Pleister
- Division of Cardiovascular Medicine (Advanced Heart Failure & Cardiac Transplant), Department of Internal Medicine, Wexner Medical Center, Davis Heart & Lung Research Institute, The Ohio State University, Suite 200, 473 West 12th Avenue, Columbus, OH 43210-1267, USA; Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine (Sleep Medicine), Department of Internal Medicine, Wexner Medical Center, Davis Heart & Lung Research Institute, The Ohio State University, Suite 200, 473 West 12th Avenue, Columbus, OH 43210-1267, USA.
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16
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Kim SJ, Pilowsky PM, Farnham MMJ. Intrathecal Intermittent Orexin-A Causes Sympathetic Long-Term Facilitation and Sensitizes the Peripheral Chemoreceptor Response to Hypoxia in Rats. J Pharmacol Exp Ther 2016; 358:492-501. [PMID: 27384072 DOI: 10.1124/jpet.116.234443] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 07/05/2016] [Indexed: 11/22/2022] Open
Abstract
Intermittent hypoxia causes a persistent increase in sympathetic nerve activity (SNA), which progresses to hypertension in conditions such as obstructive sleep apnea. Orexins (A and B) are hypothalamic neurotransmitters with arousal-promoting and sympathoexcitatory effects. We investigated whether the sustained elevation of SNA, termed sympathetic long-term facilitation, after acute intermittent hypoxia (AIH) is caused by endogenous orexin acting on spinal sympathetic preganglionic neurons. The role of orexin in the increased SNA response to AIH was investigated in urethane-anesthetized, vagotomized, and artificially ventilated Sprague-Dawley rats (n = 58). A spinally infused subthreshold dose of orexin-A (intermittent; 0.1 nmol × 10) produced long-term enhancement in SNA (41.4% ± 6.9%) from baseline. This phenomenon was not produced by the same dose of orexin-A administered as a bolus intrathecal infusion (1 nmol; 7.3% ± 2.3%). The dual orexin receptor blocker, Almorexant, attenuated the effect of sympathetic long-term facilitation generated by intermittent orexin-A (20.7% ± 4.5% for Almorexant at 30 mg∙kg(-1) and 18.5% ± 1.2% for 75 mg∙kg(-1)), but not in AIH. The peripheral chemoreflex sympathoexcitatory response to hypoxia was greatly enhanced by intermittent orexin-A and AIH. In both cases, the sympathetic chemoreflex sensitization was reduced by Almorexant. Taken together, spinally acting orexin-A is mechanistically sufficient to evoke sympathetic long-term facilitation. However, AIH-induced sympathetic long-term facilitation appears to rely on mechanisms that are independent of orexin neurotransmission. Our findings further reveal that the activation of spinal orexin receptors is critical to enhance peripheral chemoreceptor responses to hypoxia after AIH.
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Affiliation(s)
- Seung Jae Kim
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
| | - Paul M Pilowsky
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
| | - Melissa M J Farnham
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
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17
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Prabhakar NR, Peng YJ, Kumar GK, Nanduri J. Peripheral chemoreception and arterial pressure responses to intermittent hypoxia. Compr Physiol 2016; 5:561-77. [PMID: 25880505 DOI: 10.1002/cphy.c140039] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Carotid bodies are the principal peripheral chemoreceptors for detecting changes in arterial blood oxygen levels, and the resulting chemoreflex is a potent regulator of blood pressure. Recurrent apnea with intermittent hypoxia (IH) is a major clinical problem in adult humans and infants born preterm. Adult patients with recurrent apnea exhibit heightened sympathetic nerve activity and hypertension. Adults born preterm are predisposed to early onset of hypertension. Available evidence suggests that carotid body chemoreflex contributes to hypertension caused by IH in both adults and neonates. Experimental models of IH provided important insights into cellular and molecular mechanisms underlying carotid body chemoreflex-mediated hypertension. This article provides a comprehensive appraisal of how IH affects carotid body function, underlying cellular, molecular, and epigenetic mechanisms, and the contribution of chemoreflex to the hypertension.
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Affiliation(s)
- Nanduri R Prabhakar
- Institute for Integrative Physiology and Center for Systems Biology for O2 Sensing, Biological Sciences Division, University of Chicago, Illinois, USA
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18
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Jouett NP, Hardisty JM, Mason JR, Niv D, Romano JJ, Watenpaugh DE, Burk JR, Smith ML. Systolic pressure response to voluntary apnea predicts sympathetic tone in obstructive sleep apnea as a clinically useful index. Auton Neurosci 2016; 194:38-45. [DOI: 10.1016/j.autneu.2015.12.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 12/04/2015] [Accepted: 12/08/2015] [Indexed: 11/28/2022]
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19
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White DW, Shoemaker JK, Raven PB. Methods and considerations for the analysis and standardization of assessing muscle sympathetic nerve activity in humans. Auton Neurosci 2015; 193:12-21. [PMID: 26299824 DOI: 10.1016/j.autneu.2015.08.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Revised: 08/01/2015] [Accepted: 08/03/2015] [Indexed: 01/20/2023]
Abstract
The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary among studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA.
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Affiliation(s)
- Daniel W White
- The Department of Kinesiology & Nutrition, University of Illinois at Chicago, Chicago, IL, USA.
| | - J Kevin Shoemaker
- The School of Kinesiology, University of Western Ontario, London, ON, Canada
| | - Peter B Raven
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
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20
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Mifflin S, Cunningham JT, Toney GM. Neurogenic mechanisms underlying the rapid onset of sympathetic responses to intermittent hypoxia. J Appl Physiol (1985) 2015; 119:1441-8. [PMID: 25997944 DOI: 10.1152/japplphysiol.00198.2015] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 05/19/2015] [Indexed: 11/22/2022] Open
Abstract
Sleep apnea (SA) leads to metabolic abnormalities and cardiovascular dysfunction. Rodent models of nocturnal intermittent hypoxia (IH) are used to mimic arterial hypoxemias that occur during SA. This mini-review focuses on our work examining central nervous system (CNS) mechanisms whereby nocturnal IH results in increased sympathetic nerve discharge (SND) and hypertension (HTN) that persist throughout the 24-h diurnal period. Within the first 1-2 days of IH, arterial pressure (AP) increases even during non-IH periods of the day. Exposure to IH for 7 days biases nucleus tractus solitarius (NTS) neurons receiving arterial chemoreceptor inputs toward increased discharge, providing a substrate for persistent activation of sympathetic outflow. IH HTN is blunted by manipulations that reduce angiotensin II (ANG II) signaling within the forebrain lamina terminalis suggesting that central ANG II supports persistent IH HTN. Inhibition of the hypothalamic paraventricular nucleus (PVN) reduces ongoing SND and acutely lowers AP in IH-conditioned animals. These findings support a role for the PVN, which integrates information ascending from NTS and descending from the lamina terminalis, in sustaining IH HTN. In summary, our findings indicate that IH rapidly and persistently activates a central circuit that includes the NTS, forebrain lamina terminalis, and the PVN. Our working model holds that NTS neuromodulation increases transmission of arterial chemoreceptor inputs, increasing SND via connections with PVN and rostral ventrolateral medulla. Increased circulating ANG II sensed by the lamina terminalis generates yet another excitatory drive to PVN. Together with adaptations intrinsic to the PVN, these responses to IH support rapid onset neurogenic HTN.
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Affiliation(s)
- Steve Mifflin
- Department of Integrative Physiology and Anatomy, Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, Texas; and
| | - J Thomas Cunningham
- Department of Integrative Physiology and Anatomy, Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, Texas; and
| | - Glenn M Toney
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas
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21
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Mansukhani MP, Kara T, Caples SM, Somers VK. Chemoreflexes, sleep apnea, and sympathetic dysregulation. Curr Hypertens Rep 2015; 16:476. [PMID: 25097113 DOI: 10.1007/s11906-014-0476-2] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.
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Affiliation(s)
- Meghna P Mansukhani
- Sleep Medicine, Affiliated Communities Medical Center, 101 Willmar Avenue SW, Willmar, MN, USA,
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22
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Mechanism of sympathetic activation and blood pressure elevation in humans and animals following acute intermittent hypoxia. PROGRESS IN BRAIN RESEARCH 2014; 209:131-46. [PMID: 24746046 DOI: 10.1016/b978-0-444-63274-6.00007-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Sleep apnea is associated with repeated episodes of hypoxemia, causing marked increase in sympathetic nerve activity and blood pressure. Considerable evidence suggests that intermittent hypoxia (IH) resulting from apnea is the primary stimulus for sympathetic overactivity in sleep apnea patients. Several IH protocols have been developed either in animals or in humans to investigate mechanisms underlying the altered autonomic regulation of the circulation. Most of these protocols involve several days (10-40 days) of IH exposure, that is, chronic intermittent hypoxia (CIH). Recent data suggest that a single session of IH exposure, that is, acute intermittent hypoxia (AIH), is already capable of increasing tonic sympathetic nerve output (sympathetic long-term facilitation, LTF) and altering chemo- and baroreflexes with or without elevation of blood pressure. This indicates that IH alters the autonomic neurocirculatory at a very early time point, although the mechanisms underlying this neuroplasticity have not been explored in detail. The purpose of this chapter is to briefly review the effects of AIH on sympathetic LTF and alteration of autonomic reflexes in comparison with the studies from CIH studies. We will also discuss the potential central and peripheral mechanism underlying sympathetic LTF.
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23
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Burchell AE, Sobotka PA, Hart EC, Nightingale AK, Dunlap ME. Chemohypersensitivity and autonomic modulation of venous capacitance in the pathophysiology of acute decompensated heart failure. Curr Heart Fail Rep 2013; 10:139-46. [PMID: 23504401 DOI: 10.1007/s11897-013-0135-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Heart failure is increasing in prevalence around the world, with hospitalization and re-hospitalization as a result of acute decompensated heart failure (ADHF) presenting a huge social and economic burden. The mechanism for this decompensation is not clear. Whilst in some cases it is due to volume expansion, over half of patients with an acute admission for ADHF did not experience an increase in total body weight. This calls into question the current treatment strategy of targeting salt and water retention in ADHF. An alternative hypothesis proposed by Fallick et al. is that an endogenous fluid shift from the splanchnic bed is implicated in ADHF, rather than an exogenous fluid gain. The hypothesis states further that this shift is triggered by an increase in sympathetic tone causing vasoconstriction in the splanchnic bed, a mechanism that can translocate blood rapidly into the effective circulating volume, generating the raised venous pressure and congestion seen in ADHF. This hypothesis encourages a new clinical paradigm which focuses on the underlying mechanisms of congestion, and highlights the importance of fluid redistribution and neurohormonal activation in its pathophysiology. In this article, we consider the concept that ADHF is attributable to episodic sympathetic hyperactivity, resulting in fluid shifts from the splanchnic bed. Chemosensitivity is a pathologic autonomic mechanism associated with mortality in patients with systolic heart failure. Tonic and episodic activity of the peripheral chemoreceptors may underlie the syndrome of acute decompensation without total body salt and water expansion. We suggest in this manuscript that chemosensitivity in response to intermittent hypoxia, such as experienced in sleep disordered breathing, may explain the intermittent sympathetic hyperactivity underlying renal sodium retention and acute volume redistribution from venous storage sites. This hypothesis provides an alternative structure to guide novel diagnostic and treatment strategies for ADHF.
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Affiliation(s)
- Amy E Burchell
- Bristol CardioNomics Group, Bristol Heart Institute, Bristol Royal Infirmary, Bristol, BS2 8HW, UK
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24
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Bathina CS, Rajulapati A, Franzke M, Yamamoto K, Cunningham JT, Mifflin S. Knockdown of tyrosine hydroxylase in the nucleus of the solitary tract reduces elevated blood pressure during chronic intermittent hypoxia. Am J Physiol Regul Integr Comp Physiol 2013; 305:R1031-9. [PMID: 24049117 DOI: 10.1152/ajpregu.00260.2013] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Noradrenergic A2 neurons in nucleus tractus solitarius (NTS) respond to stressors such as hypoxia. We hypothesize that tyrosine hydroxylase (TH) knockdown in NTS reduces cardiovascular responses to chronic intermittent hypoxia (CIH), a model of the arterial hypoxemia observed during sleep apnea in humans. Adult male Sprague-Dawley rats were implanted with radiotelemetry transmitters and adeno-associated viral constructs with green fluorescent protein (GFP) reporter having either short hairpin RNA (shRNA) for TH or scrambled virus (scRNA) were injected into caudal NTS. Virus-injected rats were exposed to 7 days of CIH (alternating periods of 10% O2 and of 21% O2 from 8 AM to 4 PM; from 4 PM to 8 AM rats were exposed to 21% O2). CIH increased mean arterial pressure (MAP) and heart rate (HR) during the day in both the scRNA (n = 14, P < 0.001 MAP and HR) and shRNA (n = 13, P < 0.001 MAP and HR) groups. During the night, MAP and HR remained elevated in the scRNA rats (P < 0.001 MAP and HR) but not in the shRNA group. TH immunoreactivity and protein were reduced in the shRNA group. FosB/ΔFosB immunoreactivity was decreased in paraventricular nucleus (PVN) of shRNA group (P < 0.001). However, the shRNA group did not show any change in the FosB/ΔFosB immunoreactivity in the rostral ventrolateral medulla. Exposure to CIH increased MAP which persisted beyond the period of exposure to CIH. Knockdown of TH in the NTS reduced this CIH-induced persistent increase in MAP and reduced the transcriptional activation of PVN. This indicates that NTS A2 neurons play a role in the cardiovascular responses to CIH.
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Affiliation(s)
- Chandra Sekhar Bathina
- Department of Integrative Physiology, Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, Texas
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25
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Griffin HS, Pugh K, Kumar P, Balanos GM. Long-term facilitation of ventilation following acute continuous hypoxia in awake humans during sustained hypercapnia. J Physiol 2012; 590:5151-65. [PMID: 22826133 DOI: 10.1113/jphysiol.2012.236109] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
In awake humans, long-term facilitation of ventilation (vLTF) following acute intermittent hypoxia (AIH) is only expressed if CO2 is maintained above normocapnic levels. vLTF has not been reported following acute continuous hypoxia (ACH) and it is not known whether this might be unmasked by elevated CO2. Twelve healthy participants completed three trials. In all trials end-tidal pressure of CO2 was elevated 4-5 mmHg above normocapnic levels. During Trial 1 (AIH) participants were exposed to eight 4 min episodes of hypoxia. During Trial 2 (ACH) participants were exposed to continuous hypoxia for 32 min. In Trial 3 (Control) participants were exposed to euoxia throughout. To assess the contribution of the carotid body (CB) in observed ventilatory responses, CB afferent discharge before and after each trial was transiently inhibited with hyperoxia. Minute ventilation ( ˙V E) increased following all trials, but was significantly greater in Trials 1 and 2 when compared with Trial 3 (Trial 1: 4.96 ± 0.87, Trial 2: 5.07 ± 0.7, Trial 3: 2.55 ± 0.98 l min-1, P < 0.05). Hyperoxia attenuated VE to a similar extent in baseline and recovery in all trials (Trial 1: 3.0 ± 0.57 vs. 3.27 ± 0.68, Trial 2: 1.97 ± 0.62 vs. 2.56 ± 0.62, Trial 3: 2.23 ± 0.49 vs. 2.15 ± 0.55 l min-1, P > 0.05). Data are means ± SEM. In awake humans with elevated CO2, ACH evokes a sustained increase in ventilation that is comparable to that evoked by AIH. However, a gradual positive drift in ventilation in response to elevated CO2 accounts for approximately half of this apparent vLTF. Additionally, our data support the view that the CB is not directly involved in maintaining vLTF.
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Affiliation(s)
- Harry S Griffin
- School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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Golbidi S, Badran M, Ayas N, Laher I. Cardiovascular consequences of sleep apnea. Lung 2011; 190:113-32. [PMID: 22048845 DOI: 10.1007/s00408-011-9340-1] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 10/03/2011] [Indexed: 12/25/2022]
Abstract
Sleep apnea is a common health concern that is characterized by repetitive episodes of asphyxia. This condition has been linked to serious long-term adverse effects such as hypertension, metabolic dysregulation, and cardiovascular disease. Although the mechanism for the initiation and aggravation of cardiovascular disease has not been fully elucidated, oxidative stress and subsequent endothelial dysfunction play major roles. Animal models, which have the advantage of being free of comorbidities and/or behavioral variables (that commonly occur in humans), allow invasive measurements under well-controlled experimental conditions, and as such are useful tools in the study of the pathophysiological mechanisms of sleep apnea. This review summarizes currently available information on the cardiovascular consequences of sleep apnea and briefly describes common experimental approaches useful to sleep apnea in different animal models.
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Affiliation(s)
- Saeid Golbidi
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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Xing T, Pilowsky PM. Acute intermittent hypoxia in rat in vivo elicits a robust increase in tonic sympathetic nerve activity that is independent of respiratory drive. J Physiol 2010; 588:3075-88. [PMID: 20566662 DOI: 10.1113/jphysiol.2010.190454] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Acute intermittent hypoxia (AIH) elicits long-term increases in respiratory and sympathetic outflow (long-term facilitation, LTF). It is still unclear whether sympathetic LTF is totally dependent on changes in respiration, even though respiratory drive modulates sympathetic nerve activity (SNA). In urethane-anaesthetized, vagotomized mechanically ventilated Sprague-Dawley rats, we investigated the effect of ten 45 s episodes of 10% O2-90% N(2) on splanchnic sympathetic nerve activity (sSNA) and phrenic nerve activity (PNA). We then tested whether or not hypoxic sympathetic chemoreceptor and baroreceptor reflexes were changed 60 min after AIH. We found that 17 animals manifested a sustained increase of sSNA (+51.2+/-4.7%) 60 min after AIH, but only 10 of these rats also expressed phrenic LTF compared with the time controls (rats not exposed to hypoxia, n=5). Inspiratory triggered averages of integrated sSNA showed respiratory modulation of SNA regardless of whether or not phrenic LTF had developed. The hypoxic chemoreceptor reflex was enhanced by 60 min after the development of AIH (peak change from 76.9+/-13.9 to 159.5+/-24.9%). Finally, sympathetic baroreceptor reflex sensitivity increased after sympathetic LTF was established (Gainmax from 1.79+/-0.18 to 2.60+/-0.28% mmHg1). Our findings indicate that respiratory-sympathetic coupling does contribute to sympathetic LTF, but that an additional tonic increase of sympathetic tone is also present that is independent of the level of PNA. Sympathetic LTF is not linked to the change in baroreflex function, since the baroreflex appears to be enhanced rather than impaired, but does play an important role in the enhancement of the hypoxic chemoreflex.
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Affiliation(s)
- Tao Xing
- Australian School of Advanced Medicine, Macquarie University F10A, NSW 2109, Australia
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Abstract
Obstructive sleep apnea (OSA) is a common form of sleep-disordered breathing that occurs due to recurrent collapse of the upper airway with inspiration. Large epidemiologic studies have established that OSA is a risk factor for developing hypertension. The pathophysiologic mechanism of this relationship is due to the distinctive pattern of intermittent hypoxia seen in OSA. This pattern increases sympathetic tone, oxidative stress, inflammation and endothelial dysfunction. These processes can all lead to persistent elevation of blood pressure beyond the obstructive events. OSA should be considered as part of the workup of patients with hypertension. Treatment of OSA with continuous positive airway pressure has an effect on hypertension control and risk reduction of cardiovascular diseases. This review discusses the pathophysiology and causal relationship between OSA and hypertension, along with the cardiovascular effects of treatment of OSA.
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Affiliation(s)
- Aneesa M Das
- Division of Pulmonary, Critical Care, Allergy and Sleep Medicine, The Ohio State University, 201 Davis Heart & Lung Research Institute, 473 West 12th Avenue, Columbus, OH 43209, USA.
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Friedman O, Logan AG. Sympathoadrenal mechanisms in the pathogenesis of sleep apnea-related hypertension. Curr Hypertens Rep 2009; 11:212-6. [DOI: 10.1007/s11906-009-0037-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Khayat R, Patt B, Hayes D. Obstructive sleep apnea: the new cardiovascular disease. Part I: Obstructive sleep apnea and the pathogenesis of vascular disease. Heart Fail Rev 2008; 14:143-53. [PMID: 18807180 DOI: 10.1007/s10741-008-9112-z] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Accepted: 08/12/2008] [Indexed: 12/21/2022]
Abstract
Obstructive sleep apnea (OSA) is increasingly recognized as a novel cardiovascular risk factor. OSA is implicated in the pathogenesis of hypertension, left ventricular dysfunction, coronary artery disease and stroke. OSA exerts its negative cardiovascular consequences through its unique pattern of intermittent hypoxia. Endothelial dysfunction, oxidative stress, and inflammation are all consequences of OSA directly linked to intermittent hypoxia and critical pathways in the pathogenesis of cardiovascular disease in patients with OSA. This review will discuss the known mechanisms of vascular dysfunction in patients with OSA and their implications for cardiovascular disease.
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Affiliation(s)
- Rami Khayat
- The Ohio State University Sleep Heart Program, The Ohio State University, 473 W 12th Ave, Suite 105, Columbus, OH 43210, USA
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Aouad LJ, Tam K, Waters KA. Effects of acute intermittent hypercapnic hypoxia on insulin sensitivity in piglets using euglycemic clamp. Metabolism 2008; 57:1056-63. [PMID: 18640382 DOI: 10.1016/j.metabol.2008.03.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Accepted: 03/11/2008] [Indexed: 11/27/2022]
Abstract
Continuous hypoxia is associated with insulin resistance, altered glucose metabolism, and increased sympathetic nervous activity. This study examined the effect of 2 successive exposures to intermittent hypercapnic hypoxia (IHH) on glucose metabolism and insulin sensitivity in neonatal piglets. Piglets were assigned to 2 groups. One group was exposed to 2 x 90 minutes of hypercapnic hypoxia (8% O(2), 7% CO(2)), intermittently in 6-minute cycles alternating with 6-minute air. The second group was given 2 x 90 minutes of air. Blood pressure, blood gases, glucose, insulin, and lactate were measured during exposures. Insulin sensitivity was assessed using the euglycemic clamp before and after the exposures. Piglets in the IHH group exhibited reduced PO(2) (from 111.4 +/- 14.2 to 43.3 +/- 21.7), increased PCO(2) (from 33.6 +/- 1.9 to 49.4 +/- 5.4), and lactic acidosis. Compared with air, IHH decreased blood glucose (control [CON] 4.44 +/- 0.72 mmol/L vs IHH 2.67 +/- 1.2 mmol/L, P = .007), insulin (CON 12.5 +/- 7.4 microU/mL vs IHH 3.6 +/- 3.1 microU/mL, P = .03), and mean arterial pressure (CON 143.0 +/- 7.9 mm Hg vs IHH 112.5 +/- 9.5 mm Hg, P < .001) over 90 minutes. Maximal insulin-stimulated glucose disposal was not different between the groups on either day, nor was endogenous glucose production. Overall, exposure to hypoxia in an intermittent pattern reduced sympathetic drive as indicated by blood pressure and did not alter insulin sensitivity, resulting in decreases in blood glucose and insulin. We speculate that an intermittent hypoxic stimulus results in failure of initiation of compensatory responses to increased energy requirements that would usually be observed during sustained exposure to hypoxia.
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Affiliation(s)
- Leyla J Aouad
- Department of Medicine, The University of Sydney, NSW 2006, Australia
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Serebrovskaya TV, Manukhina EB, Smith ML, Downey HF, Mallet RT. Intermittent hypoxia: cause of or therapy for systemic hypertension? Exp Biol Med (Maywood) 2008; 233:627-50. [PMID: 18408145 DOI: 10.3181/0710-mr-267] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
During acute episodes of hypoxia, chemoreceptor-mediated sympathetic activity increases heart rate, cardiac output, peripheral resistance and systemic arterial pressure. However, different intermittent hypoxia paradigms produce remarkably divergent effects on systemic arterial pressure in the post-hypoxic steady state. The hypertensive effects of obstructive sleep apnea (OSA) vs. the depressor effects of therapeutic hypoxia exemplify this divergence. OSA, a condition afflicting 15-25% of American men and 5-10% of women, has been implicated in the pathogenesis of systemic hypertension and is a major risk factor for heart disease and stroke. OSA imposes a series of brief, intense episodes of hypoxia and hypercapnia, leading to persistent, maladaptive chemoreflex-mediated activation of the sympathetic nervous system which culminates in hypertension. Conversely, extensive evidence in animals and humans has shown controlled intermittent hypoxia conditioning programs to be safe, efficacious modalities for prevention and treatment of hypertension. This article reviews the pertinent literature in an attempt to reconcile the divergent effects of intermittent hypoxia therapy and obstructive sleep apnea on hypertension. Special emphasis is placed on research conducted in the nations of the former Soviet Union, where intermittent hypoxia conditioning programs are being applied therapeutically to treat hypertension in patients. Also reviewed is evidence regarding mechanisms of the pro- and anti-hypertensive effects of intermittent hypoxia.
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Leuenberger UA, Hogeman CS, Quraishi SA, Quraishi S, Linton-Frazier L, Gray KS. Short-term intermittent hypoxia enhances sympathetic responses to continuous hypoxia in humans. J Appl Physiol (1985) 2007; 103:835-42. [PMID: 17556498 DOI: 10.1152/japplphysiol.00036.2007] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Short-term intermittent hypoxia leads to sustained sympathetic activation and a small increase in blood pressure in healthy humans. Because obstructive sleep apnea, a condition associated with intermittent hypoxia, is accompanied by elevated sympathetic activity and enhanced sympathetic chemoreflex responses to acute hypoxia, we sought to determine whether intermittent hypoxia also enhances chemoreflex activity in healthy humans. To this end, we measured the responses of muscle sympathetic nerve activity (MSNA, peroneal microneurography) to arterial chemoreflex stimulation and deactivation before and following exposure to a paradigm of repetitive hypoxic apnea (20 s/min for 30 min; O(2) saturation nadir 81.4 +/- 0.9%). Compared with baseline, repetitive hypoxic apnea increased MSNA from 113 +/- 11 to 159 +/- 21 units/min (P = 0.001) and mean blood pressure from 92.1 +/- 2.9 to 95.5 +/- 2.9 mmHg (P = 0.01; n = 19). Furthermore, compared with before, following intermittent hypoxia the MSNA (units/min) responses to acute hypoxia [fraction of inspired O(2) (Fi(O(2))) 0.1, for 5 min] were enhanced (pre- vs. post-intermittent hypoxia: +16 +/- 4 vs. +49 +/- 10%; P = 0.02; n = 11), whereas the responses to hyperoxia (Fi(O(2)) 0.5, for 5 min) were not changed significantly (P = NS; n = 8). Thus 30 min of intermittent hypoxia is capable of increasing sympathetic activity and sensitizing the sympathetic reflex responses to hypoxia in normal humans. Enhanced sympathetic chemoreflex activity induced by intermittent hypoxia may contribute to altered neurocirculatory control and adverse cardiovascular consequences in sleep apnea.
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Affiliation(s)
- Urs A Leuenberger
- Division of Cardiology, MC H047, Heart & Vascular Institute, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, P.O. Box 850, Hershey, PA 17033, USA.
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Prabhakar NR, Dick TE, Nanduri J, Kumar GK. Systemic, cellular and molecular analysis of chemoreflex-mediated sympathoexcitation by chronic intermittent hypoxia. Exp Physiol 2007; 92:39-44. [PMID: 17124274 DOI: 10.1113/expphysiol.2006.036434] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Patients with recurrent apnoeas exhibit autonomic abnormalities manifested as persistent increase in sympathetic nerve activity (SNA). Several studies suggest that chronic intermittent hypoxia (CIH) resulting from recurrent apnoeas is a major stimulus for evoking autonomic morbidity. Although it has been proposed that CIH, by way of activating the chemoreceptor reflex, leads to sympathetic excitation, the underlying mechanisms are incompletely understood. Studies on experimental models have provided new insights into the mechanisms associated with CIH-evoked sympathoexcitation. The purpose of this article is to highlight recent information on systemic, cellular and molecular analysis of the effects of CIH on chemoreceptor-mediated sympathoexcitation. Chronic intermittent hypoxia exerts two major effects on the chemoreceptor reflex: (a) augmentation of the carotid body and sympathetic effector responses to acute hypoxia; and (b) induction of long-lasting activation of both the sensor and the effector that persists several hours after termination of CIH. Available evidence indicates that CIH may facilitate processing of chemoreceptor afferent information at the central nervous system. Recent studies suggest that reactive oxygen species-mediated signalling is a major cellular mechanism, and transcriptional activation by hypoxia-inducible factor-1 is one of the critical molecular mechanisms underlying chemoreceptor-mediated sympathoexcitation by CIH.
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Affiliation(s)
- Nanduri R Prabhakar
- Department of Physiology & Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44109, USA. .
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Fu Q, Townsend NE, Shiller SM, Martini ER, Okazaki K, Shibata S, Truijens MJ, Rodríguez FA, Gore CJ, Stray-Gundersen J, Levine BD. Intermittent hypobaric hypoxia exposure does not cause sustained alterations in autonomic control of blood pressure in young athletes. Am J Physiol Regul Integr Comp Physiol 2007; 292:R1977-84. [PMID: 17204591 DOI: 10.1152/ajpregu.00622.2006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intermittent hypoxia (IH), which refers to the discontinuous use of hypoxia to reproduce some key features of altitude acclimatization, is commonly used in athletes to improve their performance. However, variations of IH are also used as a model for sleep apnea, causing sustained sympathoexcitation and hypertension in animals and, thus, raising concerns over the safety of this model. We tested the hypothesis that chronic IH at rest alters autonomic control of arterial pressure in healthy trained individuals. Twenty-two young athletes (11 men and 11 women) were randomly assigned to hypobaric hypoxia (simulated altitude of 4,000-5,500 m) or normoxia (500 m) in a double-blind and placebo-controlled design. Both groups rested in a hypobaric chamber for 3 h/day, 5 days/wk for 4 wk. In the sitting position, resting hemodynamics, including heart rate (HR), blood pressure (BP), cardiac output (Q(c), C(2)H(2) rebreathing), stroke volume (SV = Q(c)/HR), and total peripheral resistance (TPR = mean BP/Q(c)), were measured, dynamic cardiovascular regulation was assessed by spectral and transfer function analysis of cardiovascular variability, and cardiac-vagal baroreflex function was evaluated by a Valsalva maneuver, twice before and 3 days after the last chamber exposure. We found no significant differences in HR, BP, Q(c), SV, TPR, cardiovascular variability, or cardiac-vagal baroreflex function between the groups at any time. These results suggest that exposure to intermittent hypobaric hypoxia for 4 wk does not cause sustained alterations in autonomic control of BP in young athletes. In contrast to animal studies, we found no secondary evidence for sustained physiologically significant sympathoexcitation in this model.
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Affiliation(s)
- Qi Fu
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, TX 75231, USA
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36
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Dick TE, Hsieh YH, Wang N, Prabhakar N. Acute intermittent hypoxia increases both phrenic and sympathetic nerve activities in the rat. Exp Physiol 2006; 92:87-97. [PMID: 17138622 DOI: 10.1113/expphysiol.2006.035758] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The respiratory system expresses multiple forms of plasticity, defined as alterations in the breathing pattern that persist or develop after a stimulus. Stimulation of breathing with intermittent hypoxia (IH) elicits long-term facilitation (LTF), a type of plasticity in which respiratory motor activity progressively increases in anaesthetized animals, even after the stimuli have ceased and blood gases have normalized. It is unknown whether the sympathetic nervous system similarly expresses IH-induced plasticity, but we predicted that IH would evoke LTF in sympathetic nerve activity (SNA) because respiratory and sympathetic control systems are coupled. To test this idea, we recorded splanchnic (sSNA) and phrenic nerve activities (PNA) in equithesin-anaesthetized rats. Animals were exposed to 10 45 s episodes of 8% O(2)-92% N(2), separated by 5 min intervals of 100% O(2), and recordings were continued for 60 min following the last hypoxic exposure. Cycle-triggered averages of integrated PNA and sSNA from periods preceding, and 5 and 60 min following the hypoxic stimuli were compared. Intermittent hypoxia significantly increased both sSNA and PNA. Treatment with methysergide (3 mg kg(-1), i.v.) 20 min before the intermittent hypoxic exposures prevented the increases in integrated PNA and sSNA 60 min after IH, indicating a role of serotonergic pathways in this form of plasticity. No increases in PNA and sSNA occurred at comparable times (60 and 120 min) in rats not exposed to hypoxia. The increased sSNA was not simply tonic, but was correlated with respiratory bursts, and occurred predominantly during the first half of expiration. These findings support the hypothesis that sympathorespiratory coupling may underlie the sustained increase in SNA associated with the IH that occurs during sleep apnoea.
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Affiliation(s)
- Thomas E Dick
- Biomedical Research Building BRB B55, 10900 Euclid Avenue, Cleveland, OH 44106-4941, USA.
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Foster GE, Poulin MJ, Hanly PJ. Intermittent hypoxia and vascular function: implications for obstructive sleep apnoea. Exp Physiol 2006; 92:51-65. [PMID: 17124276 DOI: 10.1113/expphysiol.2006.035204] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Obstructive sleep apnoea (OSA) has been implicated as a risk factor for the development of hypertension, stroke and myocardial infarction. The main cause of cardiovascular and cerebrovascular disease in OSA is thought to be exposure to intermittent hypoxia, which can lead to oxidative stress, inflammation, atherosclerosis, endothelial dysfunction and hypertension. These proposed mechanisms have been drawn from basic research in animal and human models of intermittent hypoxia in addition to clinical investigation of patients with OSA. This review outlines the association between OSA and vascular disease, describes basic mechanisms that may be responsible for this association and compares the results from studies of OSA subjects with those in experimental models of intermittent hypoxia.
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Affiliation(s)
- Glen E Foster
- Department of Medicine, Faculty of Medicine, University of Calgary, Health Sciences Center, Room 1421, 3330 Hospital Drive NW, Calgary, Alberta, Canada
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Abstract
The link between sleep apnoea and systemic hypertension in humans is well documented. However, a direct causal association between the two diseases independent of comorbidities has been difficult to establish. Comorbidities clearly play an important role in this strong relationship; however, new findings also suggest that sleep apnoea is an independent risk factor for hypertension. This relationship appears to be at least in part a result of chronically elevated sympathetic activity, and therefore manifests as a neurally mediated hypertension. Although the mechanism(s) for this causal relationship of sleep apnoea to hypertension remains ill defined, a growing body of literature suggests that autonomic dysfunction, mediated by abnormal chemoreflex control of sympathetic activity, is a potential mechanism. Abnormal chemoreflex responses to both acute and chronic apnoea or hypoxia have been demonstrated. Hypothesized mechanisms by which chemoreflex dysfunction may contribute to chronically elevated sympathetic tone and ultimately hypertension are explored in this review. Thus, this review focuses on the current evidence linking chemoreflex function to obstructive sleep apnoea and systemic hypertension in humans and provides an analysis of these data and their implications.
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Affiliation(s)
- Michael L Smith
- Department of Integrative Physiology, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA.
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Kumar GK, Rai V, Sharma SD, Ramakrishnan DP, Peng YJ, Souvannakitti D, Prabhakar NR. Chronic intermittent hypoxia induces hypoxia-evoked catecholamine efflux in adult rat adrenal medulla via oxidative stress. J Physiol 2006; 575:229-39. [PMID: 16777938 PMCID: PMC1819426 DOI: 10.1113/jphysiol.2006.112524] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Chronic intermittent hypoxia (CIH) augments physiological responses to low partial pressures of O2 in the arterial blood. Adrenal medullae from adult rats, however, are insensitive to direct effects of acute hypoxia. In the present study, we examined whether CIH induces hypoxic sensitivity in the adult rat adrenal medulla and, if so, by what mechanism(s). Experiments were performed on adult male rats exposed to CIH (15 s of 5% O2 followed by 5 min of 21% O2; 9 episodes h(-1); 8 h d(-1); for 3 or 10 days) or to comparable, cumulative durations of continuous hypoxia (CH; 4 h of 7% O2 followed by 20 h of 21% O2 for 1 or 10 days). Noradrenaline (NA) and adrenaline (ADR) effluxes were monitored from ex vivo adrenal medullae. In adrenal medullae of rats exposed to CIH, acute hypoxia evoked robust NA and ADR effluxes, whereas these responses were absent in control rats or in those exposed to CH for 1 or 10 days. Hypercapnia (10% CO2; either acidic, pH 6.8, or isohydric, pH 7.4) was ineffective in eliciting catecholamine (CA) efflux from control, CIH or CH rats. Nicotine (100 microM) evoked NA and ADR effluxes in control rats, and this response was abolished in CIH but not in CH rats. Systemic administration of 2-deoxyglucose depleted ADR content in control rats, and CIH attenuated this response, indicating downregulation of neurally regulated CA secretion. Cytosolic and mitochondrial aconitase enzyme activities decreased in CIH adrenal medullae, suggesting increased generation of superoxide anions. Systemic administration of antioxidants reversed the effect of CIH on the adrenal medulla. Rats exposed to CIH exhibited increased blood pressures and elevated plasma CA, and antioxidants abolished these responses. These observations demonstrate that CIH induces hypoxic sensing in the adult rat adrenal medulla via mechanisms involving increased generation of superoxide anions and suggest that hypoxia-evoked CA efflux from the adrenal medulla contributes, in part, to elevated blood pressure and plasma CA.
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Affiliation(s)
- Ganesh K Kumar
- Department of Biochemistry, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4935, USA.
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Wiernsperger N, Nivoit P, Bouskela E. Obstructive sleep apnea and insulin resistance: a role for microcirculation? Clinics (Sao Paulo) 2006; 61:253-66. [PMID: 16832559 DOI: 10.1590/s1807-59322006000300011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Obstructive sleep apnea is an increasingly recognized medical problem. The recent attention to its frequency in the general population and its important role in metabolic, vascular, and behavioral aspects have sharply increased the number and nature of investigations, thereby revealing new aspects that open new approaches in research. Whereas obstructive sleep apnea is a well-known phenomenon accompanying obesity and diabetes, new findings strongly suggest that this close relationship may also operate in the opposite direction. Indeed obstructive sleep apnea may be a primary feature inducing or aggravating a series of vascular and metabolic disturbances closely resembling the metabolic syndrome. This review will discuss established and potential mechanisms responsible for these changes. Obstructive sleep apnea indeed appears to gather all the elements necessary to induce insulin resistance, hypertension, and possibly heart failure. After careful analysis of these modifications and considering how they are intertwined, we propose that microcirculation could represent the common denominator mediating the progression of this pathology, as it is eventually the case in the metabolic syndrome and diabetes domain. This plausible hypothesis is discussed in detail and should be verified by appropriate preclinical and clinical protocols, which are now achievable by using noninvasive techniques in humans.
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Affiliation(s)
- Nicolas Wiernsperger
- Department of Physiological Sciences, State University of Rio de Janeiro, Brazil
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Yun AJ, Lee PY, Gerber AN. Integrating systems biology and medical imaging: understanding disease distribution in the lung model. AJR Am J Roentgenol 2006; 186:925-30. [PMID: 16554557 DOI: 10.2214/ajr.05.0072] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE Many chronic diseases exhibit characteristic pulmonary distribution patterns, but the underlying biologic explanations remain elusive. On the basis of emerging evidence from systems biology, we propose that gradients of T helper immune function exist as an epiphenomenon of the hypoxic pulmonary vasoconstriction response. Regional variation of immune function may contribute to preferential distribution patterning of lung diseases. CONCLUSION The lungs represent but one example in which the distribution of immune function throughout the body may explain disease location. This hypothetic framework can apply to diseases outside the realm of pulmonary biology and illustrates the potential benefit of integrating advances in systems biology and medical imaging.
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Affiliation(s)
- Anthony J Yun
- Department of Radiology, Stanford University, 470 University Ave., Palo Alto, CA 94301, USA.
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Monahan KD, Leuenberger UA, Ray CA. Effect of repetitive hypoxic apnoeas on baroreflex function in humans. J Physiol 2006; 574:605-13. [PMID: 16709638 PMCID: PMC1817765 DOI: 10.1113/jphysiol.2006.108977] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Baroreflex function is impaired in patients with obstructive sleep apnoea. We tested the hypothesis that short-term exposure to repetitive hypoxic apnoeas (RHA) produces prolonged impairment in baroreflex function. Baroreflex function was determined using the modified Oxford technique in 14 subjects (26 +/- 1 years). Baroreflex sensitivity (BRS) was quantified from the R-R interval-systolic blood pressure (BP; cardiovagal BRS), heart rate-systolic BP (HR BRS) and muscle sympathetic nerve activity (MSNA)-diastolic BP (sympathetic BRS) relations. RHA involved subjects performing repetitive end-expiratory apnoeas (20 s) every minute for 30 min during intermittent hypoxia to accentuate oxygen desaturation. After RHA, BP and MSNA at rest were elevated. BRS was measured approximately 7 (Post 1), approximately 30 (Post 2) and approximately 50 min (Post 3) after RHA to provide insight into the temporal pattern of responses. Cardiovagal BRS (16.8 +/- 1.3, 16.5 +/- 1.6, 17.6 +/- 2.0 and 17.4 +/- 1.5 ms mmHg(-1) for Pre, Post 1, Post 2 and Post 3, respectively), HR BRS (-1.1 +/- 0.1, -1.1 +/- 0.1, -1.3 +/- 0.1 and -1.4 +/- 0.1 beats min(-1) mmHg(-1)) and sympathetic BRS (-4.5 +/- 0.6, -4.4 +/- 0.7, -3.7 +/- 0.5 and -4.7 +/- 1.0 arbitrary units (au) beat(-1) mmHg(-1)) were unchanged by RHA. In contrast, the operating points of the baroreflexes were shifted rightward (to higher levels of BP) and upward (to higher levels of heart rate and MSNA) after RHA (P < 0.05). Time control studies performed in five additional subjects showed no change in any of the measured variables over time. Collectively, these data indicate that short-term exposure to RHA shifts ('resets') the baroreflex stimulus-response curve to higher levels of BP without influencing BRS for extended periods of time.
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Affiliation(s)
- Kevin D Monahan
- Penn State Heart and Vascular Institute, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
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Abstract
The Multiple Sleep Latency Test (MSLT) and the Maintenance of Wakefulness Test (MWT) are two commonly used laboratory-based objective tests to measure sleepiness and alertness, respectively. Data suggest both are extremely sensitive tests when measuring the effects of sleep deprivation within subjects, but are less sensitive for confirming sleepiness and response to treatment in groups of patients with different sleep disorders. Inconsistent and even sometimes paradoxical test results may be partly explained by data that show the MSLT and MWT are not selectively sensitive to either sleepiness or alertness, but sensitive to both the sleep and the arousal systems. Sleep latencies seen on both the MSLT and MWT are affected to varying degrees by a myriad of internal and external influences that can alter what we would prefer each test to show. If we continue to use these tests to measure sleepiness or alertness in patients with different sleep disorders, we need to understand more about the nature and impact of different sources of internal and external arousal so that we can better control the test environment. Improved understanding of the determinants of sleep onset is essential because excessive sleepiness has important consequences for both individuals and society.
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Affiliation(s)
- Michael H Bonnet
- Dayton Department of Veterans Affairs Medical Center, Wright State University, Dayton, OH 45428, USA.
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Madden CJ, Morrison SF. Hypoxic activation of arterial chemoreceptors inhibits sympathetic outflow to brown adipose tissue in rats. J Physiol 2005; 566:559-73. [PMID: 15878945 PMCID: PMC1464767 DOI: 10.1113/jphysiol.2005.086322] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In urethane-chloralose anaesthetized, neuromuscularly blocked, artificially ventilated rats, we demonstrated that activation of carotid chemoreceptors inhibits the elevated levels of brown adipose tissue (BAT) sympathetic nerve activity (SNA) evoked by hypothermia, by microinjection of prostaglandin E2 into the medial preoptic area or by disinhibition of neurones in the raphe pallidus area (RPa). Peripheral chemoreceptor stimulation with systemic administration of NaCN (50 microg in 0.1 ml) or with hypoxic ventilation (8% O2-92% N2, 30 s) completely inhibited BAT SNA. Arterial chemoreceptor-evoked inhibition of BAT SNA was eliminated by prior bilateral transections of the carotid sinus nerves or by prior inhibition of neurones within the commissural nucleus tractus solitarii (commNTS) with glycine (40 nmol/80 nl) or with the GABAA receptor agonist muscimol (160 pmol/80 nl; 77 +/- 10% attenuation), or by prior blockade of ionotropic excitatory amino acid receptors in the commNTS with kynurenate (8 nmol/80 nl; 82 +/- 10% attenuation). Furthermore, activation of commNTS neurones following local microinjection of bicuculline (30 pmol/60 nl) completely inhibited the elevated level of BAT SNA resulting from disinhibition of neurones in the RPa. These results demonstrate that hypoxic stimulation of arterial chemoreceptor afferents leads to an inhibition of BAT SNA and BAT thermogenesis through an EAA-mediated activation of second-order, arterial chemoreceptor neurones in the commNTS. Peripheral chemoreceptor-evoked inhibition of BAT SNA could directly contribute to (or be permissive for) the hypoxia-evoked reductions in body temperature and oxygen consumption that serve as an adaptive response to decreased oxygen availability.
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Affiliation(s)
- C J Madden
- Neurological Sciences Institute, Oregon Health and Science University, Beaverton, OR 97006, USA.
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Nishimura M. Reply. Nephrol Dial Transplant 2005. [DOI: 10.1093/ndt/gfh670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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